Most plants get nitrogen from fertilizers. Some plants can have a process called nitrogen fixing in which nitrogen from the is turned into ammonium compounds. Animals get their nitrogen from food, by eating plants and other animals.
From plants or air.
nitrogen
Most organisms obtain nitrogen in the form of nitrate (NO3-) or ammonium (NH4+). These forms of nitrogen are usually present in the soil and can be taken up by plants. Animals then obtain nitrogen by consuming plants or other animals.
Since 78.08% of the Earth's atmosphere is composed of nitrogen, yes. But it cannot be used in biological processes. The nitrogen animals use comes in the form of nitrogen compounds acquired from food. Ultimately, the nitrogen used by most living things is produced by nitrogen-fixing bacteria which do use nitrogen from the atmosphere, these compounds are then taken in and used by plants.
Nitrogen is an absolutely essential part of amino acid structure, which makes up protein. Organisms are essentially "made" of protein, that is, the structure and function of their bodies is thanks to proteins. Nitrogen also has many other uses in the body such as the synthesis of non-protein nitrogen products (Nitric oxide, a vasodilator, and GABA, a neurotransmitter just to name a few.) But protein is definitely the most important function of Nitrogen. (Thanks to Jen for this answer!)
nitrogen
The most familiar gas required by animals, including humans, is oxygen. Oxygen is essential for breathing and cellular respiration, providing energy for the body's metabolism. It is obtained through the respiratory system by inhaling air.
animals dont really need nitrogen but for plants, they need nitrogen and they get nitrogen usually in the form of nitrates or bacteria protein, by the work of nitrifying bacteria, putrefying bacteria and nitrogen fixing bacteria
The large reservoir of nitrogen that is unusable by most organisms is atmospheric nitrogen (N2). This form of nitrogen is inert and cannot be directly utilized by plants and animals. It needs to be converted into a usable form through the process of nitrogen fixation before it can be incorporated into biological molecules.
Nitrogen is the most abundant element in the Earth's atmosphere. Bacteria in the soil 'fix' the nitrogen gas into compounds which can be taken in by plants; the plants get eaten by animals & they use the nitrogen to make proteins.
Oxygen, carbon, nitrogen, and hhydrogen